Direct substrate to solder bump connection for thermal management in flip chip amplifiers

ABSTRACT

Solder bumps are placed in direct contact with the silicon substrate of an amplifier integrated circuit having a flip chip configuration. A plurality of amplifier transistor arrays generate waste heat that promotes thermal run away of the amplifier if not directed out of the integrated circuit. The waste heat flows through the thermally conductive silicon substrate and out the solder bump to a heat-sinking plane of an interposer connected to the amplifier integrated circuit via the solder bumps.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Embodiments relate to power-amplifier design, and in particular tomanaging electrothermal performance in flip-chip power-amplifier design.

SUMMARY

In an embodiment, an alternative bumping method for linear flip-chipSiGe-power-amplifier IC design implements emitter ballasting andachieves equivalent or lower thermal resistance to that obtained withdirect emitter bumping and base ballasting.

In another embodiment, the metal bump or pillars are placed adjacent tothe NPN transistor arrays that are used in the power amplifier for RFpower generation. By placing the metal in intimate contact with thesilicon substrate, the heat generated by the NPN arrays flows down intothe silicon substrate and then out the metal bump/pillar.Advantageously, the metal bump/pillar also forms an electrical groundconnection in close proximity to the NPN array and, consequently, theemitter ballast resistors can be connected to the grounding point.

In yet another embodiment, a method to provide equivalent or lowerthermal resistance for a SiGe NPN array of a power amplifier relative tothe emitter bumping method is disclosed. In an embodiment, the Cu pillarconnects directly to the bulk silicon substrate adjacent to the NPNtransistor array. The metal area and contact-via area is maximized tothe extent of the bump pad to provide less thermal resistance withoutincreasing the die area. The heat generated in each emitter stripe ofthe transistor array is more efficiently transferred to the bulk siliconrather than to the polysilicon-emitter-contact via because of thephysical differences in the top side versus the backside contact surfacearea of the integrated circuit (IC) or chip. Since the bulk silicon hasrelatively high thermal conductivity, the heat generated in the NPNtransistor array spreads quickly and is efficiently transferred to alarge silicon contact pad and Cu pillar.

In a further embodiment, the Cu pillar bump electrically and thermallyconnects to the bulk silicon and not to the emitter contact. A ballastresistor can be electrically connected and physically placed betweeneach emitter of the NPN transistor array and the bump pad, which in anembodiment, optimizes the electrothermal configuration or layout for alinear SiGe power amplifier.

According to a number of embodiments, the disclosure related to a methodto implement an emitter-ballasted amplifier in a flip chipconfiguration. The method comprises forming at least one transistor overa silicon substrate, forming a metal pillar with respect to the siliconsubstrate such that a bottom of the metal pillar is in direct contactwith the silicon substrate, and forming a first resistor in electricalcommunication with an emitter of the at least one transistor and withthe metal pillar, heat generated during operation of theemitter-ballasted amplifier being transferred through the siliconsubstrate to the bottom of the metal pillar. In an embodiment, themethod further comprises forming the metal pillar in a cavity etchedinto the silicon substrate such that the metal pillar protrudes outwardsand upwards from the cavity, the bottom and at least a portion of theside of the metal pillar in direct contact with the silicon substrate.

In an embodiment, the metal pillar is configured to provide a flip chipinterconnection for the emitter-ballasted amplifier. In anotherembodiment, the metal pillar is configured to form a part of a thermalpath for heat generated by the at least one transistor when theemitter-ballasted amplifier is operating. In a further embodiment, themetal pillar does not extend over the base of the at least onetransistor. In a yet further embodiment, the metal pillar does notextend over any significant portion of the at least one transistor.

In an embodiment, the metal pillar is configured to provide a groundconnection. In another embodiment, the method further comprises forminga second resistor in communication with a base of the at least onetransistor. In a further embodiment, the metal pillar includes copper.In a yet further embodiment, the metal pillar forms at least one solderbump of a flip chip.

In an embodiment, the at least one transistor includes an NPN bipolarjunction transistor. In another embodiment, the emitter-ballastedamplifier includes a SiGe power amplifier.

Certain embodiments relate to an emitter-ballasted amplifier comprisingat least one transistor formed over a silicon substrate, a metal pillarformed with respect to the silicon substrate such that a bottom of themetal pillar is in direct contact with the silicon substrate, and afirst resistor in communication with an emitter of the at least onetransistor and with the metal pillar, heat generated during operation ofthe at least one transistor being transferred through the siliconsubstrate to the bottom of the metal pillar. In an embodiment, theemitter-ballasted amplifier further comprises a cavity etched into thesilicon substrate, the metal pillar formed within the cavity such thatthe metal pillar protrudes outwards and upwards from the cavity, thebottom and at least a portion of the side of the metal pillar in directcontact with the silicon substrate.

In an embodiment, the metal pillar is configured to provide a flip chipinterconnection. In another embodiment, the metal pillar is configuredto form a part of a thermal path for heat generated by the at least onetransistor. In a further embodiment, the metal pillar is configured toprovide a ground connection. In a yet further embodiment, the metalpillar forms at least one solder bump of a flip chip.

According to further embodiments, the disclosure related to a wirelessmobile device comprising an antenna configured to receive and transmitradio frequency (RF) signals, a transmit/receive switch configured topass an amplified RF signal to the antenna for transmission, and amulti-chip module including a flip chip amplifier die that includes atleast one emitter-ballasted amplifier configured to amplify an RF inputsignal and to generate the amplified RF signal, where the at least oneemitter-ballasted amplifier includes at least one transistor formed overa silicon substrate, a metal pillar formed with respect to the siliconsubstrate such that a bottom of the metal pillar is in direct contactwith the silicon substrate, and a first resistor in communication withan emitter of the at least one transistor and the metal pillar, and anoutput matching network die including an output matching network circuitconfigured to match an impedance of a fundamental frequency of theamplified RF signal. In an embodiment, the at least oneemitter-ballasted amplifier further includes a second resistor incommunication with a base of the at least one transistor to providebase-ballasting.

According to a number of embodiments, the disclosure related to anamplifier die comprising an emitter-ballasted amplifier including atleast one transistor formed over a silicon substrate, a metal pillarformed with respect to the silicon substrate such that a bottom of themetal pillar is in direct contact with the silicon substrate, and afirst resistor in communication with an emitter of the at least onetransistor and with the metal pillar, where heat generated duringoperation of the at least one transistor is transferred through thesilicon substrate to the bottom of the metal pillar. The amplifier diefurther comprises an input pad electrically connected to a firstterminal of the emitter-ballasted amplifier, an output pad electricallyconnected to a second terminal of the emitter-ballasted amplifier, and aplurality of interconnections configured to electrically connect atleast the first resistor to the metal pillar. In an embodiment, aportable transceiver comprises the amplifier die.

Certain embodiments relate to a multi-chip module comprising a flip chipamplifier die including at least one emitter-ballasted amplifierconfigured to amplify an input signal and to generate an amplifiedoutput signal, where the at least one emitter-ballasted amplifierincludes at least one transistor formed over a silicon substrate, ametal pillar formed with respect to the silicon substrate such that abottom of the metal pillar is in direct contact with the siliconsubstrate, and a first resistor in communication with an emitter of theat least one transistor and with the metal pillar. Heat generated duringoperation of the at least one transistor is transferred through thesilicon substrate to the bottom of the metal pillar. The multi-chipmodule further comprises an output matching network die including anoutput matching network circuit configured to match an impedance of afundamental frequency of the amplified output signal. In an embodiment,the emitter-ballasted amplifier includes a SiGe power amplifier.

Advantages of embodiments disclosed herein include:

1. An efficient method to remove heat from a SiGe NPN power transistorarray which results in equivalent or lower thermal resistance thanemitter bumping, thereby improving power, gain, and linearity of theSiGe power amplifier.

2. Emitter ballasting instead of base ballasting for thermal stabilityand improved linearity of a SiGe power amplifier.

3. An efficient design of collector and base power combining networks.When emitter bumps are used, the collector and base of the transistorexit the array orthogonally to the emitter, which creates unequal phasedistribution between the base and collector or equal phase with lessoptimum impedance transformation networks from additional routing.

4. A straightforward conversion from chip-on-board (COB) and/orthrough-silicon-via (TSV) to flip chip (FC) package design and viceversa due to fewer changes to matching network layout and the overall ICfloor plan.

5. A low impedance substrate connection, which achieves optimumlinearity, output power, and efficiency from the NPN transistor array.

6. Superior linearity and ruggedness due to the use of emitterballasting, as base ballasting degrades amplifier performance due to thereduction in collector to emitter breakdown voltage (ruggedness),reduction in peak current (Vbe droop), and increased base band impedancewhich degrades linearity (memory effect).

7. Prevents thermal coupling between adjacent arrays. The emitter bumpremoves heat that would otherwise be transferred to adjacent transistorarrays. Removal of the heat reduces current mismatch conditions, limitsthe amount of current collapse, and reduces thermal run away of thetransistor arrays, which increases the safe operating area, increasesreliability, and increases linearity of the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary amplifying circuit, according to certainembodiments.

FIG. 2 is a schematic illustrating a base-ballasted amplifying circuit,according to certain embodiments.

FIG. 3 is a schematic illustrating an emitter-ballasted amplifyingcircuit, according to certain embodiments.

FIG. 4 illustrates an exemplary flip-chip interconnection ofsemiconductor devices, according to certain embodiments.

FIG. 5 illustrates a top view of an exemplary flip-chip amplifier layoutfor a base-ballasted amplifier, according to certain embodiments.

FIG. 6 illustrates a cross section of the base-ballasted amplifier ofFIG. 5, according to certain embodiments.

FIG. 7 illustrates a top view of an exemplary flip-chip amplifier layoutfor an emitter-ballasted amplifier, according to certain embodiments.

FIG. 8 illustrates a cross section of the emitter-ballasted amplifier ofFIG. 7, according to certain embodiments.

FIG. 9 is a schematic illustrating a base and emitter-ballastedamplifying circuit, according to certain embodiments.

FIG. 10 illustrates a top view of an exemplary flip-chip amplifierlayout for a base and emitter-ballasted amplifier, according to certainembodiments.

FIG. 11 illustrates a cross section of the base and emitter-ballastedamplifier of FIG. 10, according to certain embodiments.

FIG. 12 illustrates a perspective view of an exemplary amplifier layoutshowing Cu pillars beside transistors arrays, according to certainembodiments.

FIG. 13 illustrates another embodiment of electrothermal design foremitter-ballasted amplifiers implemented in flip chip configuration,according to certain embodiments.

FIG. 14 illustrates another embodiment of electrothermal design foremitter-ballasted amplifiers implemented in flip chip configuration,according to certain embodiments.

FIG. 15 is an exemplary block diagram of an amplifier die, according tocertain embodiments.

FIG. 16 is an exemplary block diagram of an amplifier module, accordingto certain embodiments.

FIG. 17 is an exemplary block diagram illustrating a simplified portabletransceiver including embodiments of flip-chip power amplifier layouts,according to certain embodiments.

DETAILED DESCRIPTION

FIG. 1 is a schematic of an exemplary amplifying circuit 100 comprisingan amplifier 102 that is configured to amplify an input signal Vin toprovide an amplified output signal Vout. In an embodiment, the amplifier102 comprises a power amplifier. In an embodiment, an output matchingnetwork receives the amplified output signal Vout and matches animpedance of a fundamental frequency of the amplified output signal. Inan embodiment, a front end module comprises the amplifier 102 and theoutput matching network.

In the design of bipolar power amplifier devices, ballasting is employedto limit the amount of current in the device to maintain thermalstability and achieve good electrical performance. In an embodiment,ballasting resistors electrically couple to the individual NPN cellsthat make up a power transistor array. Either base or emitter ballastingcan prevent thermal runaway and catastrophic failure of the NPN array.

FIG. 2 illustrates an embodiment of a base-ballasted amplifier 200comprising an array of 1 to N base-ballasted transistor pairs202(1)-202(n). In an embodiment, each base-ballasted transistor pair202(n) comprises a first transistor Q1 n, a second transistor Q2 n,where each transistor Q1 n, Q2 n has a base, an emitter, and acollector. Each base-ballasted transistor pair 202(n) further comprisesa first base resistor Rb1 n, a second base resistor Rb2 n, a first basecapacitor Cb1 n, and a second case capacitor Cb2 n. In an embodiment,the amplifier 200 comprises a power amplifier. In a further embodiment,the amplifier 200 comprises a SiGe power amplifier.

For each base-ballasted transistor pair 202(n), a base terminal of thefirst transistor Q1 n electrically couples to a first terminal of thefirst base resistor Rb1 n and a first terminal of the first basecapacitor Cb1 n. And a base terminal of the second transistor Q2 nelectrically couples to a first terminal of the second base resistor Rb2n and a first terminal of the second base capacitor Cb2 n.

Second terminals of the first base capacitors Cb11 through Cb1 nelectrically couple to second terminals of the second base capacitorsCb21 through Cb2 n and to each other to form an amplifier base or aninput 204 to the base-ballasted amplifier 200. In an embodiment, theinput 204 comprises an RF input.

Second terminals of the first base resistors Rb11 through Rb1 nelectrically couple to second terminals of the second base resistorsRb21 through Rb2 n and to each other and are in communication with a DCbase signal 206. In an embodiment, the DC base signal 206 comprises aground signal.

Collector terminals the first transistors Q11 through Q1 n electricallycouple to collector terminals of the second transistors Q21 through Q2 nand to each other to form an amplifier collector or an output 208 fromthe base-ballasting amplifier 200. In an embodiment, the output 208comprises an RF output.

Emitter terminals the first transistors Q11 through Q1 n electricallycouple to emitter terminals of the second transistors Q21 through Q2 nand to each other to form an amplifier emitter 210 of thebase-ballasting amplifier 200.

FIG. 3 illustrates an embodiment of an emitter-ballasted amplifier 300comprising an array of 1 to N emitter-ballasted transistor pairs302(1)-302(n). In an embodiment, each emitter-ballasted transistor pair302(n) comprises the first transistor Q1 n, the second transistor Q2 n,where each transistor Q1 n, Q2 n has a base, an emitter, and acollector. Each emitter-ballasted transistor pair 302(n) furthercomprises a first emitter resistor Re1 n, a second emitter resistor Re2n, the first base capacitor Cb1 n, and the second case capacitor Cb2 n.In an embodiment, the amplifier 300 comprises a power amplifier. In afurther embodiment, the amplifier 300 comprises a SiGe power amplifier.

For each emitter-ballasted transistor pair 302(n), the emitter terminalof the first transistor Q1 n electrically couples to a first terminal ofthe first emitter resistor Re1 n. And the emitter terminal of the secondtransistor Q2 n electrically couples to a first terminal of the secondemitter resistor Re2 n. Second terminals of the first emitter resistorsRe11 through Re1 n electrically couple to second terminals of the secondemitter resistors Re21 through Re2 n and to each other to form anamplifier emitter 310 of the emitter-ballasted amplifier 300.

Base terminals of the first transistors Q11 through Q1 n electricallycouple to base terminals of the second transistors Q21 through Q2 n, tofirst terminals of the first base capacitors Cb11 through Cb1 n, and tofirst terminals of the second base capacitors Cb21 through Cb2 n and arein communication with a DC base signal 306. In an embodiment, the DCbase signal 306 comprises a ground signal.

Second terminals of the first base capacitors Cb11 through Cb1 nelectrically couple to second terminals of the second base capacitorsCb21 through Cb2 n and to each other to form an amplifier base or aninput 304 to the emitter-ballasted amplifier 300. In an embodiment, theinput 304 comprises an RF input.

Collector terminals the first transistors Q11 through Q1 n electricallycouple to collector terminals of the second transistors Q21 through Q2 nand to each other to form an amplifier collector or an output 308 fromthe emitter-ballasting amplifier 300. In an embodiment, the output 308comprises an RF output.

For linear SiGe power amplifiers, emitter ballasting is typicallypreferred over base ballasting because base ballasting has many adverseeffects on performance, such as but not limited to, lower breakdownvoltage and poorer linearity. Emitter ballasting not only providesthermal stability but also achieves better electrical performance thanbase ballasting.

Flip chip, also known as controlled collapse chip connection or itsacronym, C4, is a method for interconnecting semiconductor devices, suchas integrated circuits or IC chips and microelectromechanical systems(MEMS), to external circuitry with solder bumps that have been depositedonto bump pads.

FIG. 4 illustrates an exemplary flip-chip assembly 400 comprising anintegrated circuit (IC) 410. In an embodiment, the IC 410 comprises anamplifier, such as, but not limited to amplifier 200, 300. In anotherembodiment, the IC 410 comprises a power amplifier. In a furtherembodiment, the IC 410 comprises a SiGe power amplifier.

Copper (Cu) pillars or solder bumps 402 are deposited on Cu solder padsor bump pads 404 on the top side of the wafer associated with the IC 410during the final wafer-processing step. In order to mount the IC 410 toexternal circuitry 406 (e.g., a circuit board or another chip or wafer),it is flipped over so that its top side faces down, and aligned so thatits Cu solder pads 404 align with matching pads 408 on the externalcircuitry 406, and then the solder is reflowed to complete theinterconnect. This is in contrast to wire bonding, in which anintegrated circuit is mounted upright, and wires are used tointerconnect chip pads to the external circuitry 406.

In power amplifier design, it is important to minimize the thermalresistance and limit the negative effects of excess heat on circuitperformance parameters, such as but not limited to power, gain, andlinearity. In flip-chip power-amplifier design, the amplifier emitters210, 310 often connect directly to a copper (Cu) pillar pad associatedwith a Cu pillar, which provides heat sinking for heat dissipation.

FIG. 5 illustrates a top view of an exemplary flip-chip amplifier layoutfor electrothermal management of a base-ballasted amplifier 500. A Cupillar 502 sits over the amplifier 500, which comprises an array 504 oftransistors Q11-Q1 n, Q21-Q2 n and a plurality of base-ballastingresistors 506.

FIG. 6 illustrates a cross section 600 of the base-ballasted amplifier500 of FIG. 5. FIG. 6 shows base-ballasted transistors Q1, Q2 of thearray 504 formed over a bulk silicon substrate 610. The base terminal ofthe transistor Q1, Q2 is in communication with the base-ballastingresistor 506. FIG. 6 further shows the emitter of the transistor Q1, Q2in communication with an emitter-contact via 602. In an embodiment, theemitter-contact via 602 comprises a polysilicon-emitter-contact via.Inter-level metals and contacts 608, in an embodiment, comprise L3metal, inter-level contacts (ILC), and L2 metal, and are incommunication with the emitter contact 602 and the Cu pillar 502. The Cupillar 502, through a Cu solder pad, is in contact with a laminateinterposer or printed circuit board 606. The laminate interposer orprinted circuit board 606 comprises the Cu solder pad, a Cu via, and aCu heat sink/ground plane 604.

Referring to FIGS. 5 and 6, in an embodiment, a solution for thermalmanagement in flip-chip power-amplifier design comprises connecting theemitter-contact via 602 to the Cu pillar 502 using all metal levels andcontact-via levels 608 available in the technology. The Cu pillar 502then connects to the heat sink/ground 604 on the laminate interposer orprinted circuit board 606. Heat is removed from the emitter throughrelatively small area polysilicon-emitter contact vias 602, whichtransition up through the inter-level metals and contacts 608 to the Cupillar 502 and to the heat sink/ground plane 604. The emitter contactarea is substantially less than that achieved with silicon bumping,which results in restricted heat flow.

For example, the Cu pillar 502, which can measure approximately 90μm×180 μm, is transitioned and reduced down to the size of thepolysilicon-emitter-contact via 602 which, in an embodiment, isapproximately 25 μm×0.4 μm or less. In certain embodiments, there may beapproximately 60 or more emitter contacts 602 made to a single Cu pillar502. The area of the inter-level metals and contacts 608 is alsoconstricted due to the presence of the collector terminals and thedesire to make robust electrical contact to the collector terminals.This reduction in metal and contact area increases thermal resistance.

While emitter ballasting would improve electrical properties of theamplifier 500, applying emitter ballasting may be impractical toimplement and it may lead to an excessive rise in the thermal resistanceand junction temperature due to the discontinuity caused by theemitter-ballasting resistor in the heat transfer path. Thus, baseballasting is used to provide thermal stability since emitter ballastingis neither possible nor desirable without causing significantdegradation in the thermal conductivity.

For at least these reasons, connecting the polysilicon emitter directlyto the Cu pillar 502 and heat sink 604 with base ballasting, instead ofthe more electrically optimal emitter ballasting, has traditionally beenthe electrothermal solution for flip-chip power-amplifier design.

Embodiments of better electrothermal design for amplifiers implementedin flip chip configuration are disclosed herein. In an embodiment, theamplifiers comprise power amplifiers. In another embodiment, theamplifiers comprise SiGe power amplifiers.

FIG. 7 illustrates a top view of an exemplary flip-chip amplifier layoutfor electrothermal management of an emitter-ballasted amplifier 700 thatcan be used for RF power generation. Amplifier 700 comprises an array704 of transistors Q11-Q1 n, Q21-Q2 n and a plurality ofemitter-ballasting resistors 708.

FIG. 8 illustrates a cross section of the emitter-ballasted amplifier700 of FIG. 7. FIG. 8 shows emitter-ballasted transistors Q1, Q2 of thearray 704 formed over a bulk silicon substrate 810. The emitter terminalof the transistor Q1, Q2 is in communication with the emitter-ballastingresistor 706, which introduces a discontinuity in the heat transfer ofthe heat generated in the emitter to the Cu pillar 702. FIG. 8 furthershows inter-level metals and contacts 808 in communication with the bulksilicon substrate 810 and the Cu pillar 702. In an embodiment, theinter-level metals and contacts 808 comprise L3 metal, inter-levelcontacts (ILC), L2 metal, and L1 metal. The Cu pillar 702, through a Cusolder pad, is in contact with the laminate interposer or printedcircuit board 806. The laminate interposer or printed circuit board 806comprises the Cu solder pad, a Cu via, and a Cu heat sink/ground plane804.

Referring to FIGS. 7 and 8, in an embodiment, a solution for thermalmanagement in flip-chip power-amplifier design comprises placing themetal bumps or Cu pillars 702 adjacent to the transistor arrays 704 andover inter-level metals and contacts 808. By placing the metal of the Cupillar 702 and the inter-level metals and contacts 808 in intimatecontact with the bulk silicon substrate 810, the heat generated by thetransistor arrays 704 flows into the silicon substrate 810, through theinter-level metals and contacts 808, and then out the Cu pillar 702which is in thermal contact with the heat sink/ground plane 804 of thelaminate interposer or printed circuit board 806.

Thus, the thermal properties of the silicon substrate 810 spread theheat to the substrate contacts, such as the inter-level metals andcontacts 808. The heat is then removed through the large area of thesubstrate contacts, to the Cu pillars 702 and then to the heatsink/ground plane 804.

The substrate contacts provided by the inter-level metals and contacts808 and the Cu pillars 702 also limit mutual heating of adjacenttransistor arrays 704, which improves many electrical characteristics,such as current uniformity, gain versus time characteristics, and thelike, of the power amplifier 700.

In another embodiment, the metal bump or Cu pillar 702 forms anelectrical ground connection to the ground plane 804, which in turnforms a grounding point through the inter-level metals and contacts 808.The Cu pillar 702 is in close proximity to the transistor array 704 and,the emitter-ballasting resistors 708 can be in communication with thegrounding point. In an embodiment, the grounding point provides emitterdegeneration inductance to maintain high gain over a temperature range.In an embodiment, the ground is located on the interposed or printedcircuit board (PCB) 406.

FIG. 9 illustrates an embodiment of a base and emitter-ballastedamplifier 900 comprising an array of 1 to N base and emitter-ballastedtransistor pairs 902(1)-902(n). In an embodiment, each base andemitter-ballasted transistor pair 902(n) comprises a first transistor Q1n, a second transistor Q2 n, where each transistor Q1 n, Q2 n has abase, an emitter, and a collector. Each base and emitter-ballastedtransistor pair 902(n) further comprises the first base resistor Rb1 n,the second base resistor Rb2 n, the first base capacitor Cb1 n, thesecond case capacitor Cb2 n, the first emitter resistor Re1 n, and thesecond emitter resistor Re2 n. In an embodiment, the amplifier 900comprises a power amplifier. In a further embodiment, the amplifier 900comprises a SiGe power amplifier.

For each base and emitter-ballasted transistor pair 902(n), the baseterminal of the first transistor Q1 n electrically couples to the firstterminal of the first base resistor Rb1 n and the first terminal of thefirst base capacitor Cb1 n. And the base terminal of the secondtransistor Q2 n electrically couples to the first terminal of the secondbase resistor Rb2 n and the first terminal of the second base capacitorCb2 n.

Second terminals of the first base capacitors Cb11 through Cb1 nelectrically couple to second terminals of the second base capacitorsCb21 through Cb2 n and to each other to form an amplifier base or aninput 904 to the base and emitter-ballasted amplifier 900. In anembodiment, the input 904 comprises an RF input.

Second terminals of the first base resistors Rb11 through Rb1 nelectrically couple to second terminals of the second base resistorsRb21 through Rb2 n and to each other and are in communication with a DCbase signal 906. In an embodiment, the DC base signal 906 comprises aground signal.

For each base and emitter-ballasted transistor pair 902(n), the emitterterminal of the first transistor Q1 n electrically couples to the firstterminal of the first emitter resistor Re1 n. And the emitter terminalof the second transistor Q2 n electrically couples to the first terminalof the second emitter resistor Re2 n. Second terminals of the firstemitter resistors Re11 through Re1 n electrically couple to secondterminals of the second emitter resistors Re21 through Re2 n and to eachother to form an amplifier emitter 910 of the base and emitter-ballastedamplifier 900.

Collector terminals of the first transistors Q11 through Q1 nelectrically couple to collector terminals of the second transistors Q21through Q2 n and to each other to form an amplifier collector or anoutput 908 from the base and emitter-ballasting amplifier 900. In anembodiment, the output 908 comprises an RF output.

In an embodiment, the base-ballasting resistor provides base resistancefor the base and emitter-ballasted amplifier 900. The base resistanceprovides RF isolation and assists with low frequency stability for theamplifier 900 under mismatched termination conditions.

FIG. 10 illustrates a top view of an exemplary flip-chip amplifierlayout for electrothermal management of a base and emitter-ballastedamplifier 1000. Amplifier 1000 comprises an array 1004 of transistorsQ11-Q1 n, Q21-Q2 n, a plurality of base-ballasting resistors 1006, and aplurality of emitter-ballasting resistors 1008.

FIG. 11 illustrates a cross section 1700 of the base andemitter-ballasted amplifier 1000 of FIG. 10. FIG. 11 shows base andemitter-ballasted transistors Q1, Q2 of the array 1004 formed over abulk silicon substrate 1710. The base terminal of the transistor Q1, Q2is in communication with the base-ballasting resistor 1006. The emitterterminal of the transistor Q1, Q2 is in communication with theemitter-ballasting resistor 1008, which introduces a discontinuity inthe heat transfer of the heat generated in the emitter to the Cu pillar1002. FIG. 11 further shows inter-level metals and contacts 1708 incommunication with the bulk silicon substrate 1710 and the Cu pillar1002. In an embodiment, the inter-level metals and contacts 1708comprise L3 metal, inter-level contacts (ILC), L2 metal, and L1 metal.The Cu pillar 1002, through a Cu solder pad, is in contact with alaminate interposer or printed circuit board 1706. The laminateinterposer or printed circuit board 1706 comprises the Cu solder pad, aCu via, and a Cu heat sink/ground plane 1704.

Referring to FIGS. 10 and 11, in an embodiment, a solution for thermalmanagement in flip-chip power-amplifier design comprises placing metalbumps or Cu pillars 1002 adjacent to the transistor arrays 1004 and overinter-level metals and contacts 1708. By placing the metal of the Cupillar 1002 and the inter-level metals and contacts 1708 in intimatecontact with a silicon substrate 1710, the heat generated by thetransistor arrays 1004 flows into the silicon substrate 1710, throughthe inter-level metals and contacts 1708, and then out the Cu pillar1002 which is in thermal contact with the heat sink/ground plane 1704 ofthe laminate interposer or printed circuit board 1706.

Thus, as described above, the thermal properties of the siliconsubstrate 1710 spread the heat to the substrate contacts, such as theinter-level metals and contacts 1708. The heat is then removed throughthe large area of the substrate contacts, to the Cu pillars 1002 and theheat sink/ground plane 1704.

In another embodiment, the metal bump or Cu pillar 1002 forms anelectrical ground connection to the ground plane 1704, which in turnforms a grounding point through the inter-level metals and contacts1708. The Cu pillar 1002 is in close proximity to the transistor array1004 and, the emitter-ballasting resistors 1008 can be in communicationwith the grounding point.

FIG. 12 illustrates a perspective view of an exemplary flip chip layoutof an amplifier 1200 showing at least Cu pillars 1202 beside transistorsarrays 1204. In an embodiment, the amplifier 1200 comprises at least oneof a power amplifier, a SiGe power amplifier, an emitter-ballastedamplifier, a base and emitter-ballasted amplifier, and a base-ballastedamplifier. FIG. 12 further illustrates the current uniformity benefitsof the design. The three copper pillars 1202 are arranged with twotransistor arrays 1204 between the left copper pillar 1202 and themiddle copper pill 1202 and with another two transistor arrays 1204between the middle copper pillar 1202 and the right copper pillar 1202.The middle pillar 1202 provides thermal sharing of the heat generated bythe transistor arrays 1204 on both sides of it. The thermal sharingpromotes uniform current density between all of the transistor arrays1204. When the currents are uniform, the amplifier 1200 exhibits morelinear performance than when the currents are not uniform.

FIGS. 13 and 14 illustrates additional embodiments of electrothermaldesign for emitter-ballasted amplifiers implemented in flip chipconfiguration.

FIG. 13 illustrates an amplifier layout of an amplifier 1300 comprisingNPN arrays 1304, a bump or Cu pillar 1302, and an emitter-ballastingresistor 1308 in communication with an emitter 1312 and the Cu pillar1302. The Cu pillar 1302 sets directly on an active silicon region 1310and adjacent to the NPN arrays 1304 to provide a more efficient thermalpath than when the back-end-of-line (BEOL) stack of metals anddielectrics are underneath the Cu pillar 1302. The BEOL stack is not asthermally conductive as the solid metal forming the bump or Cu pillar1302. By removing the BEOL stack from underneath the Cu pillar 1302, thelayout embodiment illustrated in FIG. 13 provides less thermalresistance to the thermal path than when the BEOL stack is positionedunderneath the Cu pillar 1302.

FIG. 14 illustrates an amplifier layout of an amplifier 1400 comprisingNPN arrays 1404, a bump or Cu pillar 1402, and an emitter-ballastingresistor 1408 in communication with an emitter 1412 and the Cu pillar1402. In this layout embodiment, the Cu pillar 1402 is sunk into asilicon active region 1410 and is adjacent to the NPN arrays 1404. In anembodiment, a cavity is etched into the plane of the wafer. The metalbump or Cu pillar 1402 is formed within the cavity and protrudesoutwards and upwards to provide additional thermal paths along the sidesof the Cu pillar 1402 for waste heat.

FIG. 15 illustrates an exemplary block diagram of an amplifier die 1500including an embodiment of an amplifier 1502. In an embodiment, theamplifier 1502 comprises the amplifier circuit or amplifier layout 102,200, 300, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1700.

FIG. 16 illustrates an exemplary block diagram of a module 1600including amplifier die 1500 of FIG. 15. The module 1600 furtherincludes connectivity 1602 to provide signal interconnections, packaging1604, such as for example, a package substrate, for packaging of thecircuitry, and other circuitry die 1606, such as, for exampleamplifiers, pre-filters, post filters modulators, demodulators, downconverters, and the like, as would be known to one of skill in the artof semiconductor fabrication in view of the disclosure herein. In anembodiment, the module 1600 comprises a front-end module.

FIG. 17 illustrates an exemplary block diagram illustrating a simplifiedportable transceiver 1100 including an embodiment of the amplifier 102,200, 300, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1500, 1600,1700.

The portable transceiver 1100 includes a speaker 1102, a display 1104, akeyboard 1106, and a microphone 1108, all connected to a basebandsubsystem 1110. A power source 1142, which may be a direct current (DC)battery or other power source, is also connected to the basebandsubsystem 1110 to provide power to the portable transceiver 1100. In aparticular embodiment, portable transceiver 1100 can be, for example butnot limited to, a portable telecommunication device such as a mobilecellular-type telephone. The speaker 1102 and the display 1104 receivesignals from baseband subsystem 1110, as known to those skilled in theart. Similarly, the keyboard 1106 and the microphone 1108 supply signalsto the baseband subsystem 1110.

The baseband subsystem 1110 includes a microprocessor (μP) 1120, memory1122, analog circuitry 1124, and a digital signal processor (DSP) 1126in communication via bus 1128. Bus 1128, although shown as a single bus,may be implemented using multiple busses connected as necessary amongthe subsystems within the baseband subsystem 1110. The basebandsubsystem 1110 may also include one or more of an application specificintegrated circuit (ASIC) 1132 and a field programmable gate array(FPGA) 1130.

The microprocessor 1120 and memory 1122 provide the signal timing,processing, and storage functions for portable transceiver 1100. Theanalog circuitry 1124 provides the analog processing functions for thesignals within baseband subsystem 1110. The baseband subsystem 1110provides control signals to a transmitter 1150, a receiver 1170, and apower amplifier 1180, for example.

It should be noted that, for simplicity, only the basic components ofthe portable transceiver 1100 are illustrated herein. The controlsignals provided by the baseband subsystem 1110 control the variouscomponents within the portable transceiver 1100. Further, the functionof the transmitter 1150 and the receiver 1170 may be integrated into atransceiver.

The baseband subsystem 1110 also includes an analog-to-digital converter(ADC) 1134 and digital-to-analog converters (DACs) 1136 and 1138. Inthis example, the DAC 1136 generates in-phase (I) and quadrature-phase(Q) signals 1140 that are applied to a modulator 1152. The ADC 1134, theDAC 1136, and the DAC 1138 also communicate with the microprocessor1120, the memory 1122, the analog circuitry 1124, and the DSP 1126 viabus 1128. The DAC 1136 converts the digital communication informationwithin baseband subsystem 1110 into an analog signal for transmission tothe modulator 1152 via connection 1140. Connection 1140, while shown astwo directed arrows, includes the information that is to be transmittedby the transmitter 1150 after conversion from the digital domain to theanalog domain.

The transmitter 1150 includes the modulator 1152, which modulates theanalog information on connection 1140 and provides a modulated signal toupconverter 1154. The upconverter 1154 transforms the modulated signalto an appropriate transmit frequency and provides the upconverted signalto the power amplifier 1180. The power amplifier 1180 amplifies thesignal to an appropriate power level for the system in which theportable transceiver 1100 is designed to operate. In an embodiment, thepower amplifier 1180 comprises the amplifier module 1600.

Details of the modulator 1152 and the upconverter 1154 have beenomitted, as they will be understood by those skilled in the art. Forexample, the data on connection 1140 is generally formatted by thebaseband subsystem 1110 into in-phase (I) and quadrature (Q) components.The I and Q components may take different forms and be formatteddifferently depending upon the communication standard being employed.

A front-end module 1162 comprises the power amplifier (PA) circuit 1180and a switch/low noise amplifier (LNA) circuit 1172. In an embodiment,the switch/low noise amplifier circuit 1172 comprises an antenna systeminterface that may include, for example, a diplexer having a filter pairthat allows simultaneous passage of both transmit signals and receivesignals, as known to those having ordinary skill in the art.

In an embodiment, the front-end module 1162 comprises the module 1600.In an embodiment, the amplifier circuit comprises the amplifier 102,200, 300, 500, 600, 700, 800, 900, 1000, 1200, 1300, 1400, 1700.

The power amplifier 1180 supplies the amplified transmit signal to theswitch/low noise amplifier circuit 1172. The transmit signal is suppliedfrom the front-end module 1162 to the antenna 1160 when the switch is inthe transmit mode.

A signal received by antenna 1160 will be directed from the switch/lownoise amplifier 1172 of the front-end module 1162 to the receiver 1170when the switch is in the receive mode. The low noise amplifiercircuitry 1172 amplifies the received signal.

If implemented using a direct conversion receiver (DCR), thedownconverter 1174 converts the amplified received signal from an RFlevel to a baseband level (DC), or a near-baseband level (approximately100 kHz). Alternatively, the amplified received RF signal may bedownconverted to an intermediate frequency (IF) signal, depending on theapplication. The downconverted signal is sent to the filter 1176. Thefilter 1176 comprises a least one filter stage to filter the receiveddownconverted signal as known in the art.

The filtered signal is sent from the filter 1176 to the demodulator1178. The demodulator 1178 recovers the transmitted analog informationand supplies a signal representing this information via connection 1186to the ADC 1134. The ADC 1134 converts these analog signals to a digitalsignal at baseband frequency and transfers the signal via bus 1128 tothe DSP 1126 for further processing.

The methods and apparatus described herein provide amplifier designs forelectrothermal management. In embodiments of the amplifier 102, 200,300, 700, 800, 900, 1000, 1180, 1200, 1300, 1400, 1500, 1600, 1700, thetransistors Q1, Q2, Q11-Q1 n, Q21-Q2 n comprise NPN bipolar junctiontransistors (BJTs). The amplifiers 102, 200, 300, 500, 600, 700, 800,900, 1000, 1180, 1200, 1300, 1400, 1500, 1600, 1700 can also beimplemented using different technologies, such as, but not limited toSiGe, MOS, PNP BJT, HBT, pHEMT, GaN, Gas, InGaP Gas HBT, MOSFET, SOI,Bulk CMOS, CMOS, and the like.

TERMINOLOGY

Some of the embodiments described above have provided examples inconnection with mobile phones. However, the principles and advantages ofthe embodiments can be used for any other systems or apparatus that haveneeds for power amplifier systems.

Such a system or apparatus can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products, electronic test equipment, etc. Examples of theelectronic devices can also include, but are not limited to, memorychips, memory modules, circuits of optical networks or othercommunication networks, and disk driver circuits. The consumerelectronic products can include, but are not limited to, a mobile phonesuch as a smart phone, a telephone, a television, a computer monitor, acomputer, a hand-held computer, a laptop computer, a tablet computer, apersonal digital assistant (PDA), a PC card, a microwave, arefrigerator, an automobile, a stereo system, a cassette recorder orplayer, a DVD player, a CD player, a VCR, an MP3 player, a radio, acamcorder, a camera, a digital camera, a portable memory chip, a washer,a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, amulti-functional peripheral device, a wrist watch, a clock, etc.Further, the electronic devices can include unfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novelmethods, apparatus, and systems described herein may be embodied in avariety of other forms; furthermore, various omissions, substitutions,and changes in the form of the methods and systems described herein maybe made without departing from the spirit of the disclosure. Theaccompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosure.

What is claimed is:
 1. A method to implement an emitter-ballastedamplifier in a flip chip configuration, the method comprising: formingat least one transistor over a silicon substrate; forming a metal pillarwith respect to the silicon substrate such that a bottom of the metalpillar is in direct contact with the silicon substrate; and forming afirst resistor in electrical communication with an emitter of the atleast one transistor and with the metal pillar, heat generated duringoperation of the emitter-ballasted amplifier being transferred throughthe silicon substrate to the bottom of the metal pillar.
 2. The methodof claim 1 further comprising forming the metal pillar in a cavityetched into the silicon substrate such that the metal pillar protrudesoutwards and upwards from the cavity, the bottom and at least a portionof a side of the metal pillar in direct contact with the siliconsubstrate.
 3. The method of claim 1 wherein the metal pillar isconfigured to provide a flip chip interconnection for theemitter-ballasted amplifier.
 4. The method of claim 1 wherein the metalpillar is configured to form a part of a thermal path for heat generatedby the at least one transistor when the emitter-ballasted amplifier isoperating.
 5. The method of claim 4 wherein the metal pillar does notextend over a base of the at least one transistor.
 6. The method ofclaim 4 wherein the metal pillar does not extend over any significantportion of the at least one transistor.
 7. The method of claim 1 whereinthe metal pillar is configured to provide a ground connection.
 8. Themethod of claim 1 further comprising forming a second resistor incommunication with a base of the at least one transistor.
 9. The methodof claim 1 wherein the metal pillar includes copper.
 10. The method ofclaim 1 wherein the metal pillar forms at least one solder bump of aflip chip.
 11. The method of claim 1 wherein the at least one transistorincludes an NPN bipolar junction transistor.
 12. The method of claim 1wherein the emitter-ballasted amplifier includes a silicon-germaniumpower amplifier.
 13. An emitter-ballasted amplifier comprising: at leastone transistor formed over a silicon substrate; a metal pillar formedwith respect to the silicon substrate such that a bottom of the metalpillar is in direct contact with the silicon substrate; and a firstresistor in communication with an emitter of the at least one transistorand with the metal pillar, heat generated during operation of the atleast one transistor being transferred through the silicon substrate tothe bottom of the metal pillar.
 14. The emitter-ballasted amplifier ofclaim 13 further comprising a cavity etched into the silicon substrate,the metal pillar formed within the cavity such that the metal pillarprotrudes outwards and upwards from the cavity, the bottom and at leasta portion of a side of the metal pillar in direct contact with thesilicon substrate.
 15. The emitter-ballasted amplifier of claim 13wherein the metal pillar is configured to provide a flip chipinterconnection.
 16. The emitter-ballasted amplifier of claim 13 whereinthe metal pillar is configured to form a part of a thermal path for theheat generated by the at least one transistor.
 17. The emitter-ballastedamplifier of claim 13 wherein the metal pillar is configured to providea ground connection.
 18. The emitter-ballasted amplifier of claim 13wherein the metal pillar forms at least one solder bump of a flip chip.19. A wireless mobile device comprising: an antenna configured toreceive and transmit radio frequency signals; a transmit/receive switchconfigured to pass an amplified radio frequency signal to the antennafor transmission; and a multi-chip module including a flip chipamplifier die that includes at least one emitter-ballasted amplifierconfigured to amplify a radio frequency input signal and to generate theamplified radio frequency signal, the at least one emitter-ballastedamplifier including at least one transistor formed over a siliconsubstrate, a metal pillar formed with respect to the silicon substratesuch that a bottom of the metal pillar is in direct contact with thesilicon substrate, and a first resistor in communication with an emitterof the at least one transistor and the metal pillar, and an outputmatching network die including an output matching network circuitconfigured to match an impedance of a fundamental frequency of theamplified radio frequency signal.
 20. The wireless mobile device ofclaim 19 wherein the at least one emitter-ballasted amplifier furtherincludes a second resistor in communication with a base of the at leastone transistor to provide base-ballasting.